The present invention relates to a hydraulic variable control apparatus for heavy construction equipment which is capable of variably controlling hydraulic fluid being supplied to an actuator.
More particularly, the present invention relates to a hydraulic variable control apparatus having inside a block of a reversing valve an auxiliary hydraulic control valve controlling hydraulic fluid flowing in and out of a hydraulic cylinder to reduce the number of parts for less costs, and capable of being used in a narrow place with preventing layout interferences when designing due to a compact structure thereof, and to be employed in a narrow space.
As schematically shown in FIG. 1, a conventional hydraulic control apparatus for heavy construction equipment is provided with a hydraulic pump 200 connected to an engine, a hydraulic cylinder 300 connected to the hydraulic pump 200 and driven by supplied hydraulic fluid, a reversing valve 100 mounted between the hydraulic pump 200 and the hydraulic cylinder 300 and for controlling hydraulic fluid to start, stop, and direction-switch the hydraulic cylinder 300, and an auxiliary hydraulic control valves 400(400A and 400B) mounted in load lines 6A and 6B between the reversing valve 100 and the hydraulic cylinder 300 to restrain hydraulic fluid being supplied to the hydraulic cylinder 300 and control a driving speed thereof.
A reference numeral 4 not described denotes a center bypass line, and 500 a relief valve draining hydraulic fluid to a tank T when a load occurs which excesses a pressure set in the circuit.
Accordingly, if an operator manipulates a control lever(not shown), a pilot signal pressure is applied to the right end of the reversing valve 100 and switches an inner spool to the left direction. With this, the hydraulic fluid discharged from the hydraulic pump 200 is supplied to the large chamber of the hydraulic cylinder 300 via a pump line 5, the switched reversing valve 100, and the load line 6A, and, at the same time, the hydraulic fluid discharged from a small chamber 31 of the hydraulic cylinder 300 returns to the tank T via a check valve 405B and the load line 6B, so the hydraulic cylinder 300 is activated extended.
In the meantime, when the reversing valve 100 is switched to the right direction of the drawing, the hydraulic fluid discharged from the hydraulic pump 200 is supplied to the small chamber 301 of the hydraulic cylinder 300, so the hydraulic cylinder 300 is activated retracted.
Depending on work conditions, in case of restraining the hydraulic fluid supplied to the hydraulic cylinder 300 and controlling an operation speed of the hydraulic cylinder 300, the auxiliary hydraulic control valve 400A can control the hydraulic fluid flowing in the large chamber 302 due to a pressure difference between pilot pressures 402A and 403A corresponding to an opening amount of a throttle 401A and a pre-set valve spring 404A.
However, the hydraulic control apparatus as stated above requires an extra block to install the auxiliary hydraulic control valve 400 in a hydraulic line between the load lines 6A and 6B of the reversing valve 100 and the hydraulic cylinder 300, causing a problem that its cost increase due to the increase of the number of parts and it is not available in a place of narrow space due to layout interferences when designing.
Further, the auxiliary control valve 400 is not provided with a check function for preventing reverse flows in case that a load pressure on the side of the hydraulic cylinder 300 is higher than a discharge pressure on the side of the hydraulic pump 200, so there is a problem of mounting an extra check valve 3 in the pump line 5 of the reversing valve 100.
Accordingly, it is an object of the present invention to provide a hydraulic control apparatus having inside a block of a reversing valve an auxiliary hydraulic control valve controlling hydraulic fluid to reduce the number of parts for less costs, and capable of being used in a narrow place with preventing layout interferences when designing due to a compact structure thereof.
It is another object of the present invention to provide a hydraulic control apparatus performing a check function of reverse flow preventions which has an excellent response when a discharge pressure of a hydraulic pump is higher than a load pressure of a working device to enhance reliability thereof.
It is yet another object of the present invention to provide a hydraulic circuit using a hydraulic control apparatus for heavy construction equipment, capable of constantly supplying set hydraulic fluid to an actuator regardless of variations of a load pressure of a working device and a pressure of the hydraulic pump.
In order to achieve the above objects, in a hydraulic control apparatus for heavy construction equipment having an actuator driven in connection to a pump line of a hydraulic pump, a hydraulic control valve mounted to a hydraulic line between the hydraulic pump and the actuator and switched upon an application of a pilot signal pressure to control flows of hydraulic fluid, and a seat valve body mounted in a hydraulic line between the pump line and hydraulic feeders to control hydraulic fluid supplied to the actuator and to auxiliarily control hydraulic fluid flowing in a load line, a hydraulic control apparatus according to the present invention comprises the seat valve body having a first seat valve displaced by a difference between a load pressure of the load line and a discharge pressure of the hydraulic pump in the hydraulic line between the pump line and the feeder lines, and varying an opening area between the pump line and the feeder lines based on a displacement amount thereof, a second seat valve displacing with respect to the first seat valve to press an elastic unit inserted between the first seat valve and the second seat valve and determining a displacement amount of the first seat valve; and a pilot spool having a pilot variable throttle, and controlling an opening degree of the pilot variable throttle with switching and determining a displacement amount of the second seat valve.
According to a preferred embodiment of the present invention, the first seat valve has a variable control throttle varying an opening area from the pump line to the feeder lines based on a displacement amount of the first seat valve, the second seat valve is provided with an auxiliary variable control throttle that an outer circumferential surface of the second seat valve is tiltedly formed with respect to a housing of the seat valve body, and varies an opening area between the outer circumferential surface of the second seat valve and the housing of the seat valve body based on a displacement amount of the second seat valve.
The pilot spool may be switched upon an application of the pilot signal pressure, or switched by a difference between signal pressures before and after main variable throttles mounted between the load line and a port of the hydraulic cylinder.
Further, a reverse flow-preventing check valve is mounted in the pilot signal pressure line formed in the seat valve body to prevent a load pressure in the load line from reverse flows to the pump line upon activating the hydraulic cylinder.